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  <script>
    // arguments 动态参数 只存在于 函数里面
    //   是伪数组 里面存储的是传递过来的实参
    function fn(){
      let sum = 0
      for(let i =0;i<arguments.length;i++){
        sum += arguments[i]
      }
      return sum
    }
    console.log(fn(1,2,3,4,5,6,7,8,9)) // 45
    
  </script>
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